1. Field of the Invention
The present invention relates to a doctoring device for an apparatus designed to apply a liquid or viscid medium onto a moving base surface.
2. Description of the Related Art
A doctoring device for a coating applicator is, for example, known from German patent document no. DE 42 09 566 A 1. In typical designs, the coater rod bed, per FIG. 6 of DE 42 09 566 A 1, includes a blade-like coater rail which is positioned in an opening in the coater beam. In this opening, the coater rail is embedded on a pressure-elastic cushion which provides an elastic support structure for the coater rail tangentially to the base surface. Furthermore, the opening in the coater beam also bears a pressure hose which supports the coater rail directionally perpendicular to the base surface. The pressure in this hose can be controlled so that the spring rate of the pressure hose can be adjusted.
Principally, it is desired to apply a coating of the liquid or viscid medium onto the base surface as uniformly as possible. This applies to the longitudinal direction as well as the transverse direction of the base surface. Especially in the transverse direction, the coating quality is adversely impacted by gravity or thermally-related deformation of the coater beam.
Insofar as these deformations only occur in a direction perpendicular to the base surface, the well-known design configuration shown on German patent document no. DE 42 09 566 A 1 provides an effective remedy. The ability to control the pressure in the pressure hose provides an optimum tuning of the spring rate to match the degree of deformation and, thus, the desired contact pressures between the coater rail and the base surface. It has been shown, however, that deformations that occur during operation of the coater apparatus not only develop in a direction perpendicular to the base surface, but also in other directions. The pressure-elastic cushion, per the design shown in German patent document no. DE 42 09 566 A1, provides inadequate remedy to overcome this problem. Due to this problem, local non-uniform pressure conditions can develop between the coater rail and the base surface in the transverse direction of the base surface. This results in a non-uniform coating profile.